Webmaster level: All
In December 2011 we announced annotations for sites that target users in many languages and, optionally, countries. These annotations define a cluster of equivalent pages that target users around the world, and were implemented using rel-alternate-hreflang link elements in the HTML of each page in the cluster.
Based on webmaster feedback and other considerations, today we’re adding support for specifying the rel-alternate-hreflang annotations in Sitemaps. Using Sitemaps instead of HTML link elements offers many advantages including smaller page size and easier deployment for some websites.
To see how this works, let's take a simple example: We wish to specify that for the URL http://www.example.com/en, targeting English language users, the equivalent URL targeting German language speakers http://www.example.com/de. Up till now, the only way to add such annotation is to use a link element, either as an HTTP header or as HTML elements on both URLs like this:

Briefly, the new Sitemaps tags shown in bold function in the same way as the HTML link tags, with both using the same attributes. The full technical details of how the annotations are implemented in Sitemaps, including how to implement the xhtml namespace for the link tag, are in our new Help Center article.
A more detailed example can be found in our new Help Center article, and if you need more help, please ask in our brand new internationalization help forum.Written by Pierre Far, Webmaster Trends Analyst